Drop private argument for include/import role

Since ansible 2.8 dropped private argument is not supported anymore:
https://github.com/ansible/ansible/issues/45038

Change-Id: I3f277ce4c785b379dbfc76a11759b6d35c1dccea

tasks/main.yml

@@ -66,7 +66,6 @@
 - name: Run the systemd service role
   include_role:
     name: systemd_service
-    private: true
   vars:
     systemd_after_targets: "{{ service_var.after_targets | default(['syslog.target', 'network.target']) }}"
     systemd_user_name: "{{ octavia_system_user_name }}"